(a) Field of the Invention
The present invention relates to an automatic transmission for a vehicle. More particularly, the present invention relates to a hydraulic control system of an eight-speed automatic transmission for a vehicle.
(b) Description of the Related Art
Typical automatic transmissions include a torque converter and a powertrain of a multiple speed gear mechanism connected to the torque converter. In addition, a hydraulic control system is provided at an automatic transmission for selectively operating at least one operational element included in the powertrain according to a running state of a vehicle.
Such an automatic transmission includes a powertrain and a hydraulic control system. The powertrain includes a compound planetary gear set, formed by combining at least two simple planetary gear sets to achieve the required multiple speeds, and a plurality of friction members. The hydraulic control system selectively operates the friction members of the powertrain according to driving conditions.
A variety of such powertrains and hydraulic control systems have been developed by vehicle manufacturers according to their own schemes. Currently, four-speed automatic transmissions are most often found on the market. However, a five or six speed automatic transmission has also been realized for enhancement of performance of power transmission and for enhanced fuel mileage of a vehicle.
Recently developed automatic transmissions achieve eight forward speeds for better performance and fuel efficiency of a vehicle, and therefore, it is required for provide a hydraulic control system for such eight-speed automatic transmission that provides a precise control and enhanced durability of the transmission.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.